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Doubled TDI pin on WROVER KIT schematic, why?
Posted: Fri Jul 14, 2017 2:01 pm
by KanyeKanye
On ESP-WROVER-KIT_SCH, JTAG section, TDI pin is doubled: one connected to MTDI (IO12/SD_DATA2), one by transistor Q3 made to heel down on a start off.
Is it designed to work like that? What if I wont apply Q3 transistor and TDI will be just connected to IO12.
As far I understand, JTAG conflicts with SD card?
Re: Doubled TDI pin on WROVER KIT schematic, why?
Posted: Sat Jul 15, 2017 1:28 am
by WiFive
I am not sure what S_TDI jumper is for other than maybe if module is type WROOM and SD card pullup is used then it can pull down strapping pin at boot. Actually that doesn't make sense as it is tied to 3v3 not EN so it would work only for poweron.
Need documentation on jumpers.
Re: Doubled TDI pin on WROVER KIT schematic, why?
Posted: Wed Dec 20, 2017 12:14 am
by charma
TDI (GPIO12) functions as a strapping pin and needs to be pulled down when the ESP32 is reset to select a 3.3V LDO output for the flash memory.
This circuit on S_TDI, when jumpered to TDI, will pull TDI/IO12 on the ESP32 low during a power-on reset.
An important distinction is that this circuit will be inactive when you press the reset button after the WROVER board has been powered up, so the state of TDI/GPIO12 can be influenced by external hardware connected to that pin.